Brazing paste



Patented Sept. 4, 1951 i int-.3395

Louis c. Kllnker, Griffith, ma, assignor to The Glidden Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application July 27,1949,

i .Serial No. 107,140

This invention relates to improvedfurnace brazing pastes. i

A wide variety of fabricated assemblies of various metals-alloys and metallic compounds melting appreciably above copper have been brazed heretofore by pre-positioning copper within or close to the Joint to be brazed and then passing the assembly through a furnace in which it-is heated to above the melting point of copper while being maintained in a reducing atmosphere. Under such conditions, the pre-positloned copper melts and is drawn by capillary action across the interface of the joint, thereby joining the parts of the assembly together through a copper bond. After the assembly has been cooled, preferably while maintained in a reducing atmosphere, a strong joint is obtained. This type of process has come to be known by the-"term "furnace brazing. It has been found .over the course of many years of experience that such furnace brazing operations produce best results when the joint clearance (i. e., the clearance betweenthe parts of the assembly which are to be joined) is less bounding the joint. This caplllaryaction is of sumcient magnitude that the pri rpositioned copper does not have to be in immediatecontact with the whole of the joint which is to be brazed. pAllthat is required is that the pre-positioned copper,- when molten, contact at least a part of the joint. Capillary action then draws the molten copper into the whole of the joint (if enough copper has been supplied initially). The merits of furnace brazing processes are well understood in the art, and need little further explanation beyond pointing out that the metals, alloys, and metal compounds which have been so brazed include cast and wrought irons and steels, stainless steels, nickel, tungsten, and various metallic carbides.

In carrying out the furnace brazingprocesses in the past, the pre-positioned copper has been provided in the form of slugs, copper foil, preformed shapes of copper wire or strip, or sometimes in the form of a copper-powderpaste in which copper powder is mixed with a vehicle such as water, alcohol, thinned nitrocellulose, or ordinary machine oil. Various disadvantages are found in the use of slugs, foils, or shaped wires or strips, since each requires that the particular shape needed for each joint of the entire assembly be cut, sheared, stamped. bent or, otherwise .'8 Claims. ((11. 148-22) formed to fit its particular joint. Such forming.

operations may involve considerable expense.

Moreover, when such formed shapes are used, it

is necessary for an operator to pick up one pf;

such shapes and carefully position it in the assembly at the place where it is wanted. -Fre-.

quently in pickingv up such a shape (e. g. a wire ring which is not fully closed), it becomes en-.-

tangled with other pieces of the same shape, and time must be spent in untangling it from the others before it can be placed in the assembly.

The time so lost may become a serious cost item;

where high rates of production are relied on to keep unit brazing costs low.

Brazing pastes have not been used as eaten sively in the past as have the pre-formed shapes; and generally have been used more on an experi;

mental basis than otherwise, being used only where the more reliable foil or slug insert or pre-formedshape of wire or strip could not be applied. The pastes have not been regarded with favor because (a) they may dry out before where it is not wanted, (0) because the vehicle,

when carbonaceous, leaves a carbon residue which may interfere with the formation of a strong joint, or which must becleaned off of the brazed assembly before the assembly can be further finished'ie. g. as by electroplating it with a desired.

finishing metal), or (d)' because the pastes of the past have in most instances been diflicult to keep powder in a synthetic hydrocarbon carrier of.

certain characteristics hereinafter described, which paste can be used in place of all of the previously used forms of copper, whether foil,

slugs, pre-formed wire or strip shapes, or copper-,

powder pastes. My improved pastels substantially non-settling, is easily applied'i'n predeteb mined quantities from suitable piston-type or pneumatic applicators, or by other devices, stays in place on the assembly while the latter is being heated in the brazing furnace, provides metallic copper which is drawn readily into the capillary joints, leaves little carbon residue, andforms a assemblies, instead of stocking. as previously, a separate supply of copper for. each particularassembly which is being brazed. Moreover when copper oxide is used to supply the brazing copper,

the cost of such copper is considerably cheaper than is copper powder or than is the wrought copper in such forms as foil, wire and strip. In addition, I have found that the vehicle of my paste is harmless to the controlled atmospheres employed in furnace brazing, and permits assemblies to be brazed in any of the conventional iur-= temperatures below about 500 G. into monomeric nace atmospheres without causing discoloration;

carburization, decarburization or other chemical alterations of the surfaces.

Accordingly, it is an object of this invention to provide a brazing paste of the type described having the properties and characteristics described. It is another object to provide an improved brazing paste composed essentially of copper oxide, copper or other joining metal suspended and dispersed in an organic vehicle, which paste leaves substantially no carbon deposit in the finished brazed joint. I y y a it is afurther object to provide'an improved brazing paste of the type-last describedfabove which includes a substantially non-'carboni'zing fllm forining" material. I

These an'dother objects will be understood from the following description of the invention.

we've found that a brazing paste having the advantages, characteristics and properties noted above can be prepared by dispersing copper oxide, metallic copper powder or powders of other join ing metals or alloys in a gellike organic polymeri c vehicle which is characterizedby being heatfdepolymerizable so as to have low Conrad son carbon values. Bolym ericfvehicles having this combination of characteristics -produce a paste in which the copper or copper oxide is substantially non-settling, and which leaves substantially no carbon deposit on assemblies brazed 1 or soldered in conventional furnace-brazing at} mospheres. Petroleum vehicles have been used heretoforein brazing pastes, but tothe best of my knowledge, the vehicles whichhave been used did not possess this combination of properties. Ordinary machine oil has been used, but the viscosity, of such oil is not great enough to avoidsettling, and it decomposes inthe brazing furnace to depositconsiderable amounts of carbon.

1 have found that synthetic petroleum jellies are'suitable for use as the vehicle in my pastes, and I prefer to use them because of their uniformity of composition and their low C'onradson carbon residues. Suchsynthetic jellies generally haveConradson'carbon values below about 0.5 and have viscosities on the order of 65 seconds (Saybolt-Universal) at 210 F. Other hydrocarb011, jellies of comparable viscosity and carbon value are equally suitable but-are'nqt presently available commercially with the consistent uniforniity of the synthetic products.

. 'Itjwill be understood that a row Conradsonfcarbpn value implies that the petroleum product, While cracking, forms volatile products at the tejmperautre's' employed in theConradson test, instead of'cracking to products which deposit cs;- b n-,. ;The te is-d ib n the -HS 1-: Btandards,"1'946, part III-"'A, at page 120 under 4 the A. S. T. M. designation 13189-46. The synthetic hydrocarbon jellies are polymerized hydrocarbons, and the processes which are employed in their preparation separate from them such products as are prone to carbonize at the temperatures involved. Hence when such synthetic products are heated in a brazing furnace, they decompose again into their more volatile monomers, dimers. etc. without being cracked appreciably to such an extent as to deposit carbon. Many other organic vehicles having similar characteristics maybe used as well. Broadly, the vehicles contemplated are the heat-depolymerizableorganic polymers which are normally gels at room temperature and are capable of being -Z6D01ymqrized; upon moderate heating, such as at or low molecular weight compounds which at suchtemperatures are vapors.

Various solvents, thinners or diluents may be used to vary the ultimate consistency of the finished paste, but the materials used for that pur-. pose should preferably be volatile below about 500 C, without decomposing to produce any sub:- stantial amountof carbonaceous residue. For

exampie, solvents such as ethylene glycol menus ethylether acetate, diethylene glycol monoethyl ether acetatefbenzene, certain higher alcohols, are useful. Various petroleum solvents or synthetic'hydrocarbon polymer oils may be used to thin" the synthetic hydrocarbon polymeric solids orgels. The solvents, thinners, or diluents may be employed in' varying-amounts as found to be necessary to form a'composition ranging in c'on-' sist'ency from astur paste to a paint-like liquid,

due regardbeing'given to the effect of the dispersed copperor copper oxide on the consistency of the final product.

it will be understood that when the brazing composition, after being applied to the assembly which is to be brazed, is heated in the reducing atmosphere of the brazing furnace, the solvents, thinners or diluents evaporate and the organic polymeric vehicledepolymerizes to low molecular or monomeric, state in which it vaporizes readily.

Therefore, substantially no part of the organic vehicle decomposes to leave a residue of carbon.

in the joint or its'immediate vicinity; Such de-- composition ncce'ssarily'occurs before the melting point of the copper powder is reached so'that' the atmosphere or the brazing furnace has free 7 access to all parts of the intended joint and c-an accomplish its function of reducing any metallic oxide films thereon and providing clean metallic surfaces which the ultimately molten copper can wet and. braze.

The relative proportions between copper oxide, copper or other joining metal powder and poly meric vehicle may be varied rather widely al though itis -preferable to include as much copper tent as highasj possible so that the amoun of; vehicle employed "will "be a minimum, "since the Gen vehicle serves no purpose in the brazing furnace other than that of keeping the joining metal in its intended position in the vicinity of the joint. It is not intended to function as a reducing'agent for any copper or other oxide which may be in the paste since such reduction may lead to decomposition and carbonization of the volatile monomers or of the other low molecular weight products resulting from heat-depolymerization of the organic vehicle. Some reduction may occur; however, most of the reduction of the copper oxide tends to occur at temperatures above the effective heat-depolymerization temperature of the polymeric vehicle, bein effected" either by iron or other metals of the assembliesbeing brazed, or by the reducing atmosphere of the furnace, or both. 9

Under some circumstances encountered in brazing plant operations, an assembly may be prepared for brazing a day or more ahead of the time at which it enters the brazing furnace. During this time interval, non-drying brazing pastes may be accidentally displaced from their intended positions on the assembly. To overcome this it is desirable under such circumstances to add a film-forming material to the past so as to make a paste which in the course of a few hours or so of exposure will dry or set to at least a soft, tenacious film. In recent years synthetic unsaturated drying hydrocarbon polymer oils of low Conradson carbon values have become available, and I particularly prefer to use such polymer oils as the film-forming ingredient.

The following example illustrates the principles of my invention.

Example One gallon of past was made by thoroughly mixing 20 lbs. of bright red cuprous oxide into 4 lbs. of a synthetic polymeric heat-depolymerizable hydrocarbon jelly. The mixture was. stirred for about one hour to produce a smooth paste. The polymeric hydrocarbon vehicle was prepared from an unctuous jelly-like synthetic hydrocarbon material having the characteristics of a petrolatum. Its properties were as follows:

A. P. I. gravity clegrees appr 33.0 Flash, F. minimum appr 350.0 Fire, F. minimum do 400.0 Viscosity S. U. at 210 F do 65 Melting point, "F 115/125 Conradson carbon per cent appr .19

The petrolatum was thinned by blending with about 8 parts thereof about 2 parts of a synthetic polymeric heat-depolymerizable hydrocarbon oil having the followin properties:

This vehicle, and others having Conradson carbon values below about .5% and preferably below about .25%, may be used with a variety of other joining-metal powders such as brass powder.

powders of low melting silver solders, powders of binary phosphorus-copper brazing alloys, powders of ternary or more complex phosphorus-copper brazing alloys, powders of silver-rich silver alloys, powders of nickel-silver alloys and other spelter solders, powders of cadmium-nickel solders, powders of soft solders, etc. Any metallic solders or brazing metal which can be produced in the formof a powder can be used to make soldering or brazing pastes in accordance with my invention.

Havin described the claimed is:.. .1

1. A substantially non-setting furnace brazing paste comprising essentially a minor amount of a polymeric; heat-depolymerizable hydrocarbon gel vehicle characterized by having a Com'adson carbon value below about 5%, and a major amount of finely-divided copper oxide dispersed in said vehicle.

2. A pastegas claimed in claim 1 wherein the Conradson carbon value is below about 25%, and wherein the-organic gel vehicle is composed of synthetic polymeric heat-depolymerizable hydrocarbon materials.

3. A substantially non-setting joining-metal paste comprising essentially: a minor amount of a synthetic'polymeric 'heat-depolymerizable hydrocarbon gel vehicle having a Conradson carbon value below about 5%; and a major amount of joining-metal powder dispersed in said vehicle.

4. A paste as claimed in claim 3 wherein the Conradson carbon value of said vehicle is below about .25%. -j

5. A paste as claimed in claim 4 wherein the joining-metal powder is a copper-base powder.

6. A paste as claimed in claim 4 wherein said vehicle includes sufficient synthetic unsaturated heat-depolyifnerizable hydrocarbon drying oil to cause saidpaste to dry on exposure to air to at least a soft coherent film.

7. A furnace brazing paste composed essentially of: about 4 parts by weight of a gel vehicle composed of synthetic polymeric heat-depolymerizable hydrocarbon materials; and about 20 parts by weight of finely-divided red cuprous oxinvention, what is 1 ide dispersed uniformly in said vehicle.

8. A paste as claimed in claim 7 which includes sufficient synthetic polymeric heat-depolymerizable unsaturated hydrocarbon drying oil in said vehicle to cause said paste to dry on exposure to air to at least a soft coherent film.

LOUIS G. KLINKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

3. A SUBSTANTIALLY NON-SETTING JOININT-METAL PASTE COMPRISING ESSENTIALLY: A MINOR AMOUNT OF A SYNTHETIC POLYMERIC HEAT-DEPOLYMERIZABLE HYDROCARBON GEL VEHICLE HAVING A CONRADSON CARBON VALUE BELOW ABOUT 5%; AND A MAJOR AMOUNT OF JOINING-METAL POWDER DISPERSED IN SAID VEHICLE. 